The present application relates to water-flushable and biodegradable films that are useful as backsheets for disposable absorbent articles, especially as backsheets for certain catamenial products.
Disposable absorbent articles currently find widespread use in many different applications, including diapers and training pants for infants and children, feminine care products such as sanitary napkins or tampons, adult incontinence products, and health care products such as surgical drapes or wound dressings. The typical disposable absorbent article usually comprises a topsheet, a backsheet and an absorbent core positioned between the backsheet and the topsheet. These products can also include a fastening system for fitting the product onto the wearer.
Depending on the type of use involved, disposable absorbent articles can be subjected to one or more insults from aqueous liquids such as water, urine, menses or blood. As a result, the backsheet materials of these disposable products are typically made of liquid impermeable materials, such as polypropylene or polyethylene films, that exhibit sufficient strength and handling capability so that the disposable absorbent article retains its integrity during use by the wearer and does not allow leakage of the liquid from the product.
Many disposable absorbent articles can be difficult to dispose of into an aqueous environment. For example, attempts to flush many disposable absorbent articles down the toilet can cause blockage of the toilet or pipes connecting the toilet to the sewage system. In particular, the backsheet materials typically used in these disposable absorbent articles generally do not dissolve, disintegrate or disperse readily when flushed down a toilet so that the disposable absorbent article cannot be disposed of in this manner. If the backsheet materials are made very thin in order to reduce the overall bulk of the disposable absorbent article so as to reduce the likelihood of blockage of the toilet or sewage pipe, the backsheet material will typically not exhibit sufficient strength to prevent tearing or ripping as the outer cover material is subjected to the stresses of normal use by the wearer.
In a number of instances, it would be desirable to be able to flush these disposable absorbent articles down the toilet. These include certain catamenial products known as labial or interlabial sanitary napkins or pads that have a portion which at least partially resides within the wearer""s vestibule and a portion which at least partially resides external to the wearer""s vestibule. Interlabial pads have the potential to provide greater freedom from inconvenience because of their small size and reduced risk of leakage. Indeed, these interlabial pads are small enough to be easily flushed down the toilet, typically without clogging it or the sewage pipes it leads to. However, even though flushable, such products could put a significant environmental demand on sewage treatment or septic tank systems if they are not readily susceptible to degradation and disintegration after being flushed.
To solve this problem, PCT application 96/20831 (Larson), published Jul. 11, 1996, discloses a film that is alleged to be substantially dispersed when contacted with an excess amount of water and can be used as a backsheet in a disposable absorbent article to increase its flushability in a liquid sewage system. This film comprises a water-dispersible layer and a barrier layer. The water-dispersible layer comprises a water-dispersible polymer such as polyethylene oxide or polyvinyl alcohol and optionally a non-water dispersible polymer to improve the strength and handling properties of this layer. The barrier layer is typically prepared from a polymer that forms a film that is liquid impermeable such as acrylic acid copolymers, and biodegradable polymers polylactic acid, polycaprolactone and polyhydroxybutyrate/hydroxyvalerate, and optionally a water-dispersible polymer in order to improve the decomposition properties of the barrier layer.
It has been found that the polymers used in these respective water-dispersible and barrier layers need to be carefully selected and formulated to provide the desired mechanical properties for such films, as well as to allow these films to be made by conventional film forming techniques, such as coextrusion. Some desirable mechanical properties for such films include sufficient tensile modulus, strength and extensibility to allow the film to be stretched and elongated without tearing or ripping, as well as sufficient softness and flexibility so that disposable products made from the film are comfortable for the wearer and do not create excessive noise during use. There is also the potential for undesired mold growth to occur if biodegradable polymers are present in film, especially if the film is exposed to high humidity and heat. Also, due to the inherent properties of water-dispersible polymers such as relatively low molecular weight (Mw), they can impart poor mechanical properties to the resultant film and undesirable stickiness when wet.
A potential problem with these films comprising both water-dispersible and barrier layers is the ability to control the degradation and disintegration rate of the film, especially when in use. In disposable absorbent articles where such films are used as backsheets, the water-dispersible layer is most likely to be exposed to aqueous liquid insults during use by the wearer. As a result, the film comprising such a layer could lose integrity over time before it is disposed of and thus potentially lead to a problem such as ripping or tearing of the film that could cause leakage.
Accordingly, it would be desirable to be able to provide a flushable and biodegradable film that could be useful as a backsheet for disposable absorbent articles, especially flushable products such as interlabial catamenial products, has desirable mechanical properties including the ability to be stretched and elongated without tearing or ripping, sufficient softness and flexibility to provide comfort for the wearer without excessive noise generation during use, does not promote undesired mold growth or cause undesired stickiness when wet during use, can be made with conventional film-forming techniques, such as coextrusion, and has controlled rates of degradation and disintegration in the presence of aqueous environments so that the film maintains sufficient integrity during use.
The present invention relates to films which are water-flushable and biodegradable. These films comprise:
a. a substantially biodegradable layer, which comprises:
(1) from about 65 to 100% of a substantially water-insoluble biodegradable thermoplastic polymer;
(2) from 0 to about 35% of a substantially water-soluble thermoplastic polymer;
b. a substantially water-soluble layer adjacent the biodegradable layer, which comprises:
(1) from about 60 to 100% of a substantially water-soluble thermoplastic polymer;
(2) from 0 to about 40% of a substantially water-insoluble biodegradable thermoplastic polymer;
c. optionally, but preferably, a substantially water-permeable layer adjacent the water soluble layer, which comprises:
(1) from about 30 to about 70% of a substantially water-soluble thermoplastic polymer;
(2) from about 30 to about 70% of a substantially water-insoluble biodegradable thermoplastic polymer;
d. wherein the amount of water-soluble thermoplastic polymer in the water-soluble layer is greater than the amount of water-soluble thermoplastic polymer in the water-permeable layer;
e. wherein the water-soluble layer is substantially thicker than each of the biodegradable and water-permeable layers.
The films of the present invention have extremely desirable mechanical properties including the ability to be stretched and elongated without tearing or ripping, and sufficient softness and flexibility to provide comfort for the wearer without excessive noise generation during use. The films of the present are also breathable with typically relatively high Moisture Vapor Transmission Rates (MVTR). Although the films of the present invention contain biodegradable polymers, they do not promote mold growth, even in the presence of humid and hot environments. Films of the present invention can also be made with conventional film forming techniques, including coextrusion, laminating and coating.
The films of the present invention are particularly useful as backsheets for disposable absorbent articles, and in particular for flushable interlabial pads. Even when wet, the films of the present invention typically do not cause undesired stickiness during use of the absorbent article. The optional water-permeable layer is particularly preferred for films of the present invention used as backsheets. This water-permeable layer controls the rate of disintegration and degradation of the film in the presence of aqueous environments during use so that the film maintains sufficient integrity, yet allows the film to be readily disintegrated after it is flushed.